Sarcoplasmic protein degradation system besides lysosomal system has been suggested to exist in muscle. Several neutral and alkaline proteases have been reported in sarcoplasmic or myofibrillar fractions, which, however, do not explain most of protein degradation in muscle. In the sarcoplasmic fraction of muscle, we found and partially purified an alkaline protease with the molecular weight of greater 500,000 daltons. This research is to purify and characterize this new enzyme, to find out how this is involved in the degradation of sarcoplasmic and myofibrillar proteins. Main points of this research will be; 1) This activity cannot be found in crude sarcoplasm fraction but only after column fractionation. Thus suggested, an inhibitor will be sought in muscle extract. 2) Similar high molecular protease (HMP) been described in liver and reticulocytes, where HMP was suggested to be involved in ATP-dependent protein degradation which was supposedly composed of multi-factors (Hershko, et al., 1979; Murakami, et al., 1980). This research will study on how inactive HMP (as it is in crude extract) is activated as one of multicomponents of ATP-dependent protein degradation. This will characterize the mechanism of ATP-requirement in protin degradation. 3) Substrate specificity of HMP for sarcoplasmic and myofibrillar proteins will be studied using purified HMP or ATP-dependent system reconstructed with HMP and other components.